You are Here: Home >< Maths

# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by Zacken)

Because it's asking for the probability that the mean number of calls in the five minute interval, that is, you want to find a distribution for the mean number of alls. This means you need to use the CLT, it's not a basic poisson at all, that would be find the probability that the number of calls (see that I didn't use the word mean) is less than x.

thanks! okay final question i promise, ex3D q11a asks for probability of total error, but if it said total mean error would that be different?
2. (Original post by MarcHughes)
It might help if you look at exercise 4A in the S3 Edexcel book. It's basically only used if they ask for it.
Got it thank you, its pretty obvious when they use it to be honest
3. (Original post by AakashG)
thanks! okay final question i promise, ex3D q11a asks for probability of total error, but if it said total mean error would that be different?
Yep, you'd need to use CLT.
4. (Original post by Zacken)
Yep, you'd need to use CLT.
BUT THE SOLUTIONS USE CLT FOR CALCULATING THE TOTAL ERROR EVEN THOUGH IT DOESNT SAY TOTAL MEAN ERROR

im gunna die ffs
5. (Original post by Katiee224)
Gotcha

I feel like Will from the inbetweeners when he's revising for his exam and starts doubting eveything he knows
Is this a word?

Yes... council?
6. If you get an expected value of bang on 5, do you still combine?
7. (Original post by Rkai01)
If you get an expected value of bang on 5, do you still combine?
The book says <5 so I would assume not
8. (Original post by Rkai01)
If you get an expected value of bang on 5, do you still combine?
AFAIK, no.
9. (Original post by AakashG)
BUT THE SOLUTIONS USE CLT FOR CALCULATING THE TOTAL ERROR EVEN THOUGH IT DOESNT SAY TOTAL MEAN ERROR

im gunna die ffs
Total error/n=mean so total error is nmean
10. (Original post by physicsmaths)
Total error/n=mean so total error is nmean
bro that makes so much sense! okay fine, but by that definition doesn't that total error is the same as total mean error?
11. (Original post by Zacken)
CLT is used when you want to find the distribution of the sample mean.
Let me break it down,

The central limit theorm says if you have a large sample, say you have a sample of 100 fish lengths (generally large is defined as >50). The mean of those lengths will be normally distributed. So if you were doing a hypothesis test and it says something along the lines of " 100 fishes had mean length 20 and variance 4" WITHOUT saying it is normally distributed. Then you have used to CLT to say they are normally distributed because there is so many of them.

Rule of thumb if you dont understand is that if it gives you a mean, a number of readings (100 fish lengths) and a variance, you will have used the CLT to treat it as a normal distribution.
12. (Original post by Inges)
Let me break it down,

The central limit theorm says if you have a large sample, say you have a sample of 100 fish lengths (generally large is defined as >50). The mean of those lengths will be normally distributed. So if you were doing a hypothesis test and it says something along the lines of " 100 fishes had mean length 20 and variance 4" WITHOUT saying it is normally distributed. Then you have used to CLT to say they are normally distributed because there is so many of them.

Rule of thumb if you dont understand is that if it gives you a mean, a number of readings (100 fish lengths) and a variance, you will have used the CLT to treat it as a normal distribution.
Quoted the wrong person there, I think.
13. (Original post by AmarPatel98)
Hi, just to clarify, how exactly would you set out your working for these q's to gain all the marks?
When you write Sum of O2 / E , You have to write every number your adding together, basically showing how your adding all your observed frequenices squared divided by your expected frequencies and how your taking away the original Total and then how you got the Chi-squared value. Then compared the Chi-squared value with the critical value from the table showing if its in the critical region or not. Then stating your conclusion.
14. (Original post by Zacken)
Quoted the wrong person there, I think.
damn it, thanks!
15. (Original post by Zacken)
S3 seems to be a popular module this year, weird.
Schools finally figured out it'll increase chances of their students getting better grades in FM.
16. (Original post by Zacken)
Same way that you would for a non-grouped data. Replace all the sum of x^2 or sum of x whatevs with sum of (x * frequency). It's S1 stuff, come on.
got it thnx again.
17. (Original post by Katiee224)
In what instances would we want to use the Central Limit Theorem? Like when does it come in handy?

Im worried i'm forgetting everything before the exam
Let me break it down,

The central limit theorm says if you have a large sample, say you have a sample of 100 fish lengths (generally large is defined as >50). The mean of those lengths will be normally distributed. So if you were doing a hypothesis test and it says something along the lines of " 100 fishes had mean length 20 and variance 4" WITHOUT saying it is normally distributed. Then you have used to CLT to say they are normally distributed because there is so many of them.

Rule of thumb if you dont understand is that if it gives you a mean, a number of readings (100 fish lengths) and a variance, you will have used the CLT to treat it as a normal distribution.
18. (Original post by Zacken)
S3 seems to be a popular module this year, weird.
30 people are doing it in my city, as opposed to 13 doing M3 You'd expect more people to shy away from the module after the reaction to the 2015 paper.
19. PEOPLE! Fire away questions! This is my revision since I've done all the past papers to the point where I remember the mark schemes !
20. (Original post by Katiee224)
Gotcha

I feel like Will from the inbetweeners when he's revising for his exam and starts doubting eveything he knows
To be fair, I have played FIFA when I'm supposed to be revising/just before an exam just to keep me as calm as a cool cucumber. And doubting myself, and spending time with someone I shouldn't be but not claiming to sleep with people when I haven't

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 29, 2016
Today on TSR

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University
Wed, 1 Aug '18
Poll
Useful resources

Can you help? Study help unanswered threadsStudy Help rules and posting guidelinesLaTex guide for writing equations on TSR

## Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE